High-speed bus capable of effectively suppressing a noise on a bus line

ABSTRACT

A high-speed bus includes a bus line to be connected with a bus driver and a bus receiver. Pull-up resistors are connected to both ends of the bus line for feeding a given pull-up electric potential thereto. A series resistor is further connected between the bus line and each of the bus driver and the bus receiver. The bus driver includes a series resistor and a capacitive component which are connected in series between the bus line and the ground. The bus receiver includes a waveform shaping component connected to the bus line for shaping a waveform of an inputted signal, and a receiver circuit receiving as an input thereof an output of the waveform shaping component.

BACKGROUND OF THE INVENTION:

The present invention relates to a system bus called a high-speed bus for use in a microcomputer or the like.

In the high-speed bus of this kind, the realization of faster data transmission has been demanded following the speed-up in operation of a processor or the like.

Heretofore, the high-speed data transfer has been realized by connecting pull-up resistors having the same resistance value (e.g. 56 Ω) to both ends of a system bus and feeding a given pull-up electric potential (e.g. 1.5V) to these pull-up resistors. One example of the high-speed bus is described in JP-A-6-35582.

However, the conventional high-speed bus is not capable of effectively suppressing ringing generated on a bus line due to change in input signal so that the data transfer rate is limited. Moreover, it can not effectively remove noise generated on the bus line, thereby to cause poor convergence of noise. This also limits the data transfer rate.

SUMMARY OF THE INVENTION:

It is therefore an object of the present invention to provide a high-speed bus which can effectively suppress ringing and noise generated on a bus line so as to enable faster data transfer.

It is another object of the present invention to provide a bus receiver which is suitable for the high-speed bus.

It is still another object of the present invention to provide a bus driver which is suitable for the high-speed bus.

Other objects of the present invention will become clear as the description proceeds.

According to one aspect of the present invention, there is provided a high-speed bus which comprises a bus line to be connected with a bus driver and a bus receiver, pull-up resistors connected to both ends of the bus line for feeding a given pull-up electric potential thereto, and a series resistor connected between the bus line and each of the bus driver and the bus receiver. In the high-speed bus, the bus driver comprises a series resistor and a capacitive component which are connected in series between the bus line and a ground. The bus receiver comprises a waveform shaping component connected to the bus line for shaping a waveform of an inputted signal and a receiver circuit receiving as an input thereof an output of the waveform shaping component.

According to another aspect of the present invention, there is provided a bus receiver which comprises a receiver circuit having an input portion for being connected to a bus line and a waveform shaping component connected to the input portion for shaping a waveform of an inputted signal.

According to still another aspect of the present invention, there is provided a bus driver having an output terminal connected to a bus line for driving the bus line. The bus driver comprises a series resistor and a capacitive component which are connected in series between the output terminal and a power supply having a given electric potential.

BRIEF DESCRIPTION OF THE DRAWING:

FIG. 1 is a circuit diagram showing a high-speed bus according to a first preferred embodiment of the present invention;

FIG. 2 is a circuit diagram showing a structure of one example of a bus driver which can be used in the high-speed bus shown in FIG. 1;

FIG. 3 is a graph showing a result of simulation on the high-speed bus of FIG. 1 driven by the bus driver of FIG. 2;

FIG. 4 is a circuit diagram showing a structure of one example of a bus receiver which can be used in the high-speed bus shown in FIG. 1;

FIG. 5 is a diagram showing a circuit for confirming disturbance of waveforms associated with the bus receiver shown in FIG. 4;

FIG. 6 is a diagram of waveform observation in the circuit shown in FIG. 5;

FIG. 7 is an explanatory diagram of a structure wherein the bus receiver shown in FIG. 4 is received in an LSI package;

FIG. 8 is a circuit diagram showing a structure of another example of a bus receiver which can be used in the high-speed bus shown in FIG. 1;

FIG. 9 is a circuit diagram showing a high-speed bus according to a second preferred embodiment of the present invention;

FIG. 10 is a circuit diagram showing a structure of one example of a bus driver which can be used in the high-speed bus shown in FIG. 9; and

FIG. 11 is a graph showing a result of simulation on the high-speed bus of FIG. 9 driven by the bus driver of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring now to FIG. 1, description will be made as regards a high-speed bus according to a first preferred embodiment of the present invention. The shown high-speed bus includes a bus line 23 having terminating resistors 21 and 22 connected to both ends thereof. Each of the terminating resistors 21 and 22 has a resistance value of 35 Ω. The terminating resistors 21 and 22 are connected to pull-up power supplies 24 and 25, respectively. Each of the pull-up power supplies 24 and 25 is set to 3.3V.

To the bus line 23, a plurality of open drain buffers 27 are connected via corresponding connectors 26. Each of the open drain buffers 27 can be a driver or receive Between each of the connectors 26 and the corresponding open drain buffer 27, a sending-end resistor (series resistor) 28 and a stub 29 are connected. Each sending-end resistor 28 has a resistance value of 25 Ω and is connected at a desired position between the bus line 23 and the corresponding open drain buffer 27. In practice, bus cards PKG-1, PKG-3, PKG-4, PKG-5, PKG-6 and PKG-7 each including the open drain buffer 27, the sending-end resistor 28 and the stub 29 are connected to the corresponding connectors 26, respectively.

The high-speed bus having the foregoing structure was actually prepared and its characteristic was measured. As the bus line 23, a standard bus was used. Distances d1, d2, d3, d4, d5 and d6 between the adjacent connectors 26 were set to 1.4 inches, 2.0 inches, 1.8 inches, 1.8 inches, 2.0 inches and 1.0 inch, respectively. As appreciated, a bus card was not connected to the second connector 26 from left. This is because the measured waveforms were most aggravated when the bus card was connected to the second connector 26. A length of each stub 29 was set to 1 inch.

The third bus card PKG-3 from left has a conventional open drain bus driver shown in FIG. 2 as the open drain buffer 27. The bus driver shown in FIG. 2 includes a MOS transistor 30 having a source connected to the ground and a drain working as an output terminal.

Simulation was carried out wherein a signal is sent from the bus card PKG-3 and time-domain variations of waveforms were observed at the other bus cards PKG-1, PKG-4, PKG-5, PKG-6 and PKG-7. The result was, as shown in FIG. 3, that the ringback quickly converged. Accordingly, as the ringback of the waveforms on the bus line speedily converges, the high-speed data transmission can be realized.

In the foregoing description, the resistance value of each sending-end resistor 28 is set to 25 Ω, which, however, may be adjusted in the range of about±5W in an actual device.

Turning now to FIG. 4, the description will be made as regards an example of a bus receiver which can be used as the open drain buffer 27. The shown bus receiver includes a receiver circuit 32 having an input portion 31, and a resistance component 33 connected to the input portion 31 as a waveform shaping means.

Now, a circuit shown in FIG. 5 is configured for confirming disturbance of the waveforms. In FIG. 5, a driver circuit 34 has an output portion 35 to which is connected one end of a first transmission line 36 having a characteristic of a propagation delay time ins at a characteristic impedance of 75 Ω. The other end of the first transmission line 36 is connected to one terminal of a first resistance component 37 a and one end of a second transmission line 38 having a characteristic of a propagation delay time ins at a characteristic impedance of 75 Ω. The other terminal of the first resistance component 37 a is connected to one end of a first capacitive component 37 b as a pseudo receiver circuit. The other end of the first capacitive component 37 b is connected to a ground 39. The other end of the second transmission line 38 is connected to one terminal of a second resistance component 41 a. The other terminal of the second resistance component 41 a is connected to one end of a second capacitive component 41 b. The other end of the second capacitive component 41 b is connected to a ground 42.

FIG. 6 shows trailing waveforms at respective portions of the circuit shown in FIG. 5. In FIG. 6, w1 represents a waveform at the output portion 35 of the driver circuit 34, w2 represents a waveform at the one end of the first capacitive component 37 b, and w3 represents a waveform at the one end of the second capacitive component 41 b.

From FIG. 6, it is confirmed that the trailing waveforms at the respective portions of the circuit have small disturbance. Accordingly, using the bus receiver shown in FIG. 4, a normal operation of the high-speed bus can be realized.

As shown in FIG. 7, it is preferable to dispose the bus receiver of FIG. 4 in an LSI package 43. Specifically, in FIG. 7, the receiver circuit 32 and the resistance component 33 are received within the LSI package 43.

Turning now to FIG. 8, the description will be made as regards another example of the bus receiver that can be used as the open drain buffer 27. The shown bus receiver includes a receiver circuit 32 having an input portion 31, a plurality of, i.e. first and second, resistance components 33 a and 33 b, and a selector 44 for selectively connecting the first and second resistance components 33 a and 33 b to the input portion 31 depending on an external signal at 442. The bus receiver shown in FIG. 8 can achieve an effect similar to that achieved by the bus receiver shown in FIG. 4.

Like the bus receiver shown in FIG. 4, it is also preferable to dispose the bus receiver of FIG. 8 in an LSI package. In this case, the receiver circuit 32, the first and second resistance components 33 a and 33 b and the selector 44 are received within the LSI package.

Referring now to FIG. 9, the description will be directed to a high-speed bus according to a second preferred embodiment of the present invention. Same or similar components are designated by same reference numeral as in FIG. 1 so as to omit explanation thereof. In the shown high-speed bus, each of terminating resistors 21 and 22 has a resistance value of 56 Ω, and each of pull-up power supplies 24 and 25 is set to 1.5V.

Turning now to FIG. 10, the description will be made as regards an example of a bus driver which can be used as an open drain buffer 27 similar to that of FIG. 2. The shown bus driver includes a MOS transistor 51 having a source connected to the ground, a series resistor 52 having one terminal connected to a drain of the MOS transistor 51, and a capacitive component, i.e. a capacitor 53, connected between the other terminal of the series resistor 52 and the ground. A resistance value of the series resistor 52 is set to 20 Ω, and a capacitance of the capacitor 53 is set to 10 pF. As in FIG. 2, the drain of Transistor 51 serves as an output terminal, and the gate receives a control or input voltage.

Simulation was carried out wherein the high-speed bus shown in FIG. 9 was driven using the bus driver shown in FIG. 10, and the result shown in FIG. 11 was obtained. Specifically, when a bus line 23 was driven through a third bus card PKG-3 using the bus driver shown in FIG. 10 so as to simulate time-domain variations of waveforms at the other bus cards PKG-1, PKG-4, PKG-5, PKG-6 and PKG-7, the result shown in FIG. 11 was obtained. As seen from FIG. 11, the convergence of ringback was accelerated.

As described above, since the ringback generated on the bus line can be quickly converged, the data transmission via the high-speed bus can be further accelerated.

In FIG. 10, the capacitive component 53 is directly grounded. Instead, it may be connected to a power supply which operates in an AC fashion similar to the ground. Also in this case, similar effects can be achieved.

As appreciated, in the foregoing description, the optimum values are exemplified with respect to the associated components, which may be adjusted depending on necessity in the actual circuits. 

What is claimed is:
 1. A high-speed bus comprising: a bus line to be connected with a bus driver and a bus receiver; pull-up resistors connected to both ends of said bus line for feeding an electric potential thereto; and a series resistor connected between said bus line and each of said bus driver and said bus receiver, said bus driver comprising a series resistive element and a capacitive component which are connected in series between said bus line and a ground and a transistor connected in parallel to said resistive element and capacitive component, said transistor having a gate for receiving an input signal, said bus receiver comprising: a waveform shaping component connected to said bus line for shaping a waveform of an inputted signal; and a receiver circuit receiving as an input thereof an output of said waveform shaping component.
 2. A high-speed bus as claimed in claim 1, wherein said given pull-up electric potential is set to 3.3V, each of said pull-up resistors being set to 35 Ω, each of said series resistors being set to 25 Ω.
 3. A high-speed bus as claimed in claim 1, wherein said bus driver further comprises a MOS transistor.
 4. A high-speed bus as claimed in claim 1, further comprising connectors for connecting said bus driver and said bus receiver to said bus line, respectively.
 5. A bus driver having an output terminal connected to a bus line for driving said bus line, said bus driver comprising a series resistor and a capacitive component which are connected in series between said output terminal and an electrical potential and a transistor connected in parallel to said resistor and capacitive component for receiving an input at a gate thereof.
 6. A bus driver as claimed in claim 5, wherein said series resistor has a resistance value of 20 Ω, said capacitive component has a capacitance of 10 pF.
 7. A bus driver as claimed in claim 5, wherein said transistor comprises a MOS transistor having a source grounded and a drain connected to said bus line. 